System for generating ablation profiles for laser refractive eye surgery

ABSTRACT

A laser eye surgery system includes a laser for producing a laser beam capable of making refractive corrections, an optical system for shaping and conditioning the laser beam, a digital micromirror device (DMD) for reflecting the shaped and conditioned beam toward the eye, and a computer system for controlling the mirrors of the DMD. The computer system utilizes at least one polynomial equation to generate a smooth refraction correction profile.

This application is a continuation-in-part of U.S. Ser. No. 09/524,312,filed Mar. 13, 2000, and which is hereby incorporated by referenceherein in its entirety.

The U.S. Government has a paid-up non-exclusive license in thisinvention as provided for by Grant No. R44 EY11587 awarded by theNational Eye Institute of the National Institute of Health.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates broadly to eye surgery. More particularly, thisinvention relates to refractive laser systems for eye surgery.

2. State of the Art

The laser refractive surgery (or laser keratectomy) field has rapidlygrown over the past few years with many new lasers and algorithms tocorrect human vision. Systems are now using laser wavelengths from theultraviolet (excimer) to the infrared to change the shape of the corneain a calculated pattern which makes it possible for the eye to focusproperly. For example, in the treatment of myopia, the excimer laser isused to remove or ablate tissue from the cornea in order to flatten itsshape. Infrared (IR) energy is also used by some companies to treatmyopia by reshaping the corneal tissue by a “thermal” method as opposedto ablation with the excimer wavelength. The correction of hyperopia isproduced by steepening the cornea by removing tissue at the outer edgesof the cornea (excimer) or by reshaping the cornea at the outer edges(IR energy). The correction of astigmatism, both myopic and hyperopic,requires the laser to remove or reshape tissue in a more complexpattern.

Initial systems approved by the FDA implement the refractive correctionsby a broadbeam approach; i.e., by delivering beam-shaped laser energybased on thin lens theory and paraxial optics applied to a singlespherical surface. The beam is shaped by a motorized iris (myopia andhyperopia) and a motorized slit (astigmatism) configured according toprofiles derived through Munnerlyn's derivation (C. R. Munnerlyn, S. J.Koons, and J. Marshall, “Photorefractive keratectomy: a technique forlaser refractive surgery”, J. Cataract Refract. Surg. 14, 46-52 (1988)).Referring to FIG. 1, more particularly, an excimer broadbeam laser beam10, typically having a raw rectangular shape measuring 8-10 mm by 20-25mm and shaped by optics into a 7-10 mm square or circle, is projectedonto a motorized, mechanical iris 12 to create a two dimensional (2-D)circular ablation pattern for treating myopia, and onto a motorized,mechanical slit 14 to create a 2-D rectangular ablation pattern fortreating astigmatism, and together forming the combined 2-D pattern 16.Thus, the large rectangular laser beam is shaped to form a circle or asmaller rectangle. These shapes are then projected with an imaging lens18 onto the cornea 20 of the eye 22 in a controlled manner to performthe refractive correction. To create a refractive correction, acorrectly shaped volume of tissue must be removed. Referring to FIG. 2,this volume of tissue is removed by firing a series of laser pulses (1,2, 3, . . . , n) through the iris and/or slit in a controlled fashion tocreate a three dimensional (volumetric) etch. This is the most commonmethod in the commercial market today and is currently used by VISX andSummit. Referring to FIG. 3, as a mechanical iris is used to create the“circular” part of the ablation pattern, the etch is not perfectlycircular. Physical irises possess a finite number of blades. Forexample, VISX uses a 12-leaf (12 blades) iris, while Summit used a14-leaf iris. Therefore, the resolution of the ablation patterns throughthe iris (FIG. 3) is far from the ideal (FIG. 4). Moreover, the choiceof ablation patterns (circular, rectangular, or a combination thereof),is constrained by mechanical limitations.

A more recent approach to laser keratectomy uses a scanning laser spotsystem in which a small laser spot (typically 0.5 mm to 1.0 mm indiameter) is scanned across the cornea in a predetermined pattern toachieve refractive corrections. These systems differ in that they aremore flexible than the broadbeam approach. With the control of a smallspot, different areas of the cornea can be shaped independently of otherareas. The scanning spot system has the added advantage of being able toablate smaller regions of the cornea (0.5 to 1.0 mm spot size) so it canbe directed to ablate more complex, customized patterns (as opposed tothe broadbeam approach).

Recently, corneal topography maps have been used to reveal that thecornea has many minute variations across the cornea. The broadbeam laserapproach ablates an equal amount of tissue from the high points and lowpoints of the corneal surface so that the original contour of thesurface remains (compare FIGS. 5a and 5 b which show exaggeratedvariations of a greatly enlarged minute location). The broadbeam lasercannot correct these minute variations. Initial scanning spot systemsalso failed to accommodate surface contours. Yet, the introduction ofthe scanning spot laser has allowed more controlled treatment and thuscorneal topography-driven. treatments have been produced. For thisprocedure, the surface topography of the eye is considered along withthe refraction correction profile. Thus, Munnerlyn's equation, or anyother higher order model, is combined with the eye surface topography toachieve a better refractive correction. To derive the. ablation profile,the corneal profile (topographical data), as shown in FIG. 6a, is firstdetermined from the corneal topography system measurements. Next, thetopographical data is compared to the ideal corneal shape, e.g., asphere or asphere, without correction. Referring then to FIG. 6b, thedifference between these two is determined at each x,y point in thecornea topographical data array (a digitized image). Then, a profilewhich eliminates the topographical data (hills and valleys) is generatedleaving an ideal surface after which the refraction correction ablationprofile is applied. Alternatively, the topographical differences can becombined into the refraction correction ablation profile and the entirecombined profile can be applied all at once. For either method, thescanning spot approach allows treatment in isolated areas (versusbroadbeam), and thus a pattern of spots is applied to attempt tocorrectly match the topography.

The corneal topography approach compensates only for topographicalaberrations at the corneal surface. However, the eye is a complexoptical system of which the cornea is only one component. Thus, thecurrent refraction correction equation, as derived by Munnerlyn, is notcapable of suggesting what correction must be made to the corneal shapein order to optimally correct for the overall aberration of the eye'soptical system.

There have been several recent approaches to the above problems. First,by expanding the mathematical equations for refraction correction toinclude higher order effects, coma (3rd order) and spherical (4th order)aberrations can be reduced. See C. E. Martinez, R. A. Applegate, H. C.Howland, S. D. Klyce, M. B. McDonald, and J. P. Medina, “Changes incorneal aberration structure after photorefractive keratectomy,” Invest.Ophthalmol. Visual Sci. Suppl. 37, 933 (1996). Second, by improvingschematic model eyes to include higher order aberrations, these newmodels can provide insight into how the various elements of the eyeoptical system correlate to affect visual performance. For example,there is a general consensus that the negative asphericity of the normalcornea contributes a negative aberration content. The negativeaberration is compensated for by a positive aberration contribution fromthe gradient index nature of the lens. See H. Liou and N. A. Brennan,“Anatomically accurate, finite model eye for optical modeling,” J. Opt.Soc. Am. A, Vol. 14, 1684-1695 (1997). The convergence of work onmodeling the human optical system with more accurate mathematicaldescriptions for refraction correction has led to the development ofadvanced ablation profile algorithms that treat the cornea as the firstaspheric element in an optical system. See J. Schwiegerling and R. W.Snyder, “Custom. photorefractive keratectomy ablations for thecorrection of spherical and cylindrical refractive error andhigher-order aberration,” J. Opt. Soc. Am. A, Vol. 15, No. 9, 2572-2579(1998).

Therefore, more recently, a number of wavefront sensing systems arebeing developed for the scanning spot laser refractive market. In thesesystems, a visible laser beam, or a number of visible laser beams,is/are directed through the entire eye optical system: cornea, lens,vitreous and retina. The return reflection from the retina is recordedby a CCD camera and analyzed against an ideal wavefront. Thus, theentire optical system is analyzed. The result of this analysis yields asimulation of best acuity for the patient. This data can be used to makean exact contour ablation of the cornea. Regardless of which techniqueis used, the result is a contour topographical map yielding heightinformation from the current corneal shape to the shape calculated tobest improve visual acuity with a scanning spot.

However, there are several problematic issues with all scanning spotsystems. First is the issue of treatment time. Scanning spot systemsrequire longer refractive surgery times. The scanning spot is a slowerapproach since the small laser spot has to be moved over a wide surface(up to 10 mm for hyperopia). The scanning spot system typically deliversseveral hundred spots per treatment layer, and consequently treatmenttimes are relatively long. The broadbeam approach is much quicker as theentire cornea is treated with each laser pulse, or treatment layer.

Second is the issue of safety. The broadbeam laser is inherently safefrom a treatment interruption standpoint because the cornea is treatedsymmetrically for each pulse; the iris represents a circle and the slitrepresents a rectangle so that every point on the cornea being treatedis treated the same with each laser pulse. If the procedure isinterrupted, there will always be some symmetrical spherical correctionwhich can be continued more easily at a later time. However, thescanning spot, with its small spot size, cannot cover the entire cornealsurface with one laser pulse. Thus, if an interruption occurs, there isno guarantee of a complete corneal etch for a layer at the point ofinterruption. Continuation at the point of interruption would bedifficult.

Third is the issue of tracking. In the scanning spot system the eyeneeds to be tracked very carefully in order to deliver the spot to thecorrect point on the cornea as the eye moves. This is not as much of aproblem in the broadbeam system as a broader area of the cornea istreated with each pulse.

Fourth is the issue of surface roughness. Due to the circularcross-sectional shape of the laser spot, the scanning spot techniquenecessitates overlap of the laser spot as the laser spot is moved in araster scan (left to right, top to bottom) over the cornea (see FIG. 7).While it is necessary to overlap spots to provide complete coverage fora given ablation zone (a typical 80/20 overlap is shown in FIG. 7),regions of overlap will be ablated at twice the etch depth per pulse.This tends to create roughness in the resulting etch. The roughness ofthe ablated volume is dependent on the spot overlap and to a lesserextent, the ratio of spot diameter and ablation zone diameter. Thisproblem is not seen in the broadbeam approach.

Fifth is the issue of resolution. The laser spot typically has adiameter of between 0.5 mm and 1 mm. However, corneal topography andwavefront sensor analysis provide detailed information about therequired correction to the cornea, and such details may require ablationat a resolution greater than 0.5 mm. For example, referring to FIG. 8a,both corneal topography and wavefront sensor analysis provide imageswhich defines several topography zones requiring ablation. One suchtopography zone is, isolated in FIG. 8b. Yet, referring to FIGS. 8c and8 d, neither a 1 mm spot or a 0.5 mm spot, respectively, are sized toablate the topography zone at the desired resolution.

In response to the problems associated with the current broadbeam andscanning spot system, U.S. Pat. No. 5,624,437 to Freeman, which ishereby incorporated by reference herein in its entirety, discloses theuse of a digital micromirror device (DMD) to redirect a broadbeam laserpulse to the eye. The DMD includes over a million individuallyconfigurable mirrors each having a square reflective surface 13 or 16microns per side. The mirrors are configurable into refractivecorrection patterns of very high resolution, and the laser energy isreflected by the mirrors into appropriate corrective patterns on theeye. The system has none of the disadvantages associated with priorbroadbeam and scanning spot systems, but the advantages of each areprovided.

In view of the superior resolution capable with the Freeman DMD lasersystem; it is desirable to utilize a DMD laser system which is adaptableto perform any type of laser ablative pattern: broadbeam circular andrectangular patterns, scanning spot circular and rectangular patterns,corneal topography patterns, and wavefront sensor analysis patterns.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a DMD-refractivelaser system which can recreate in relatively higher resolution any ofthe ablation patterns currently used in broadbeam and spot scanningsystems.

It is another object of the invention to provide a control system for aDMD-refractive laser system which configures the mirrors of the DMD intorefractive correction patterns.

It is a further object of the invention to provide a control systemwhich is adapted to permit a DMD to be utilized with current broadbeamlasers, enabling such lasers to refractively correct the optical systemof the eye with greater resolution, speed, and accuracy.

It is an additional object of the invention to provide a control systemfor a DMD-refractive laser system which can be operated in either ofbroadbeam or scanning spot modes.

In accord with these objectives a laser eye surgery system according tothe invention includes a laser for producing a laser beam capable ofmaking refractive corrections, an optical system for shaping andconditioning the laser beam, a DMD for reflecting the shaped andconditioned beam toward the eye, a computer system for controlling themirrors of the DMD, and an eye tracking system which tracks the positionof the eye and provides feedback to the computer system. According tothe invention, the computer system includes system software whichpermits the DMD to emulate the patterns and laser beam control providedin prior art broadbeam systems and scanning spot systems. In view of theabove, the laser surgery system is adaptable to perform every currentlyused. approach to laser surgery. That is, as the techniques arecontrolled by software in the computer system coupled to the DMD, thesystem is not limited by hardware requirements, and via configuration ofthe software, a single laser surgery system may be used to operateaccording to any of the above described approaches. Moreover, the lasersurgery system can be coupled to or adapted to receive data from cornealtopographers or wavefront sensor systems and utilize such data toincrease the quality of correction. Furthermore, the laser surgerysystem provides much greater resolution than prior art systems as theindividual mirrors of the DMD are 13 or 16 microns in size,substantially smaller than the smallest scanning spots.

Additional objects and advantages of the invention will become apparentto those skilled in the art upon reference to the detailed descriptiontaken in conjunction with the provided figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a prior art broadbeam refractive laser systemusing an iris/slit approach;

FIG. 2 is a schematic illustrating the prior art process of laseretching the cornea;

FIG. 3 is a schematic of various size openings available with a priorart 12-leaf mechanical iris for defining laser ablation patterns.;

FIG. 4 is a schematic of ideal iris openings for creating laser ablationpatterns;

FIGS. 5a and 5 b are exaggerated illustrations of corneal topographiesbefore and after broadbeam laser ablation;

FIG. 6a is an enlarged and exaggerated cross-section of a corneaillustrating topographical roughness of the cornea;

FIG. 6b is an enlarged and exaggerated cross-section of the cornea ofFIG. 6a in which areas above an ideal curvature are ablated and areasbelow ideal curvature are not ablated so that a refractive correctionetch may be performed thereafter;

FIG. 7 illustrates the raster scan operation and spot overlap of ascanning spot laser system;

FIG. 8a is a three dimensional image defining several topography zonesrequiring ablation;

FIG. 8b is an image of one of the topography zones of FIG. 8a;

FIG. 8c illustrates a method of scanning a 1 mm diameter spot over thetopography zone of FIG. 8b;

FIG. 8d illustrates a method of scanning a 0.5mm diameter spot over thetopography zone of FIG. 8b;

FIG. 9 is a schematic of a DMD laser refractive surgery system utilizingthe control system of the invention;

FIG. 10 is a schematic of a DMD mirror array circular pattern;

FIG. 11 is a schematic of a DMD mirror array circular rectangular orslit pattern;

FIG. 12 is a flowchart for using a broadbeam laser system in associationwith a DMD to correct the shape of the cornea;

FIG. 13 illustrates the multiple zones used in the multiple zonemultiple pass algorithm;

FIG. 14 is an exemplar screen print for a myopic treatment using thesoftware of the DMD laser surgery system of the invention;

FIG. 15 is a schematic of a DMD ring-shaped pattern mirror array forhyperopic refractive correction;

FIG. 16 is an exemplar screen print for an astigmatic treatment usingthe software of the DMD laser surgery system of the invention;

FIG. 17 is a screen print illustrating the volumetric ablation resultingfrom a multiple zone, multiple pass algorithm;

FIG. 18 illustrates a random scanning method for emulation of a scanningspot laser system with the laser surgery system of the invention;

FIG. 19 illustrates a polar scanning method for the DMD laser surgerysystem of the invention;

FIG. 20 illustrates a polar scanning method with rotation for the DMDlaser surgery system of the invention;

FIG. 21 illustrates a closed-pack scanning method for the DMD lasersurgery system of the invention;

FIG. 22 is a flowchart for emulating a scanning spot approach with thelaser surgery system and a corneal topographer;

FIG. 23 is a flowchart for performing laser eye surgery in an approachutilizing corneal topography data and optimized for a DMD; and

FIG. 24 illustrates the etch resolution provided by the proceduredescribed in FIG. 23 with respect to the topography zone illustrated inFIG. 8b;

FIG. 25 is a flowchart for performing laser eye surgery in an approachutilizing wavefront sensor data and optimized for a DMD;

FIG. 26a illustrates a 3-D ablation image according to a preferredmultizone single pass (MZSP) broadbeam approach;

FIG. 26b illustrates a smooth ablation profile according to a preferredMZSP broadbeam approach;

FIG. 27 is a graph illustrating profiles of classifications of degreesof corrections;

FIG. 28 is a graph illustrating sixth order of magnitude trendlineswhich follow the contours of the profiles of FIG. 27; and

FIG. 29 is a graph illustrating the substantially linearity of thetrendlines for the sixth order magnitude equations for eachclassification based on diopter correction, and a polynomial equationbased on thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIG. 9, a laser eye surgery system 100 includes a laser102 for producing a laser beam capable of making refractive corrections,an optical system 104 for shaping and conditioning the laser beam, adigital micromirror device (DMD) 106 for reflecting the shaped andconditioned beam toward the eye 108, a computer system 110 forcontrolling the mirrors of the DMD 106, and an eye tracking system 112which tracks the position of the eye 108 and provides feedback to thecomputer system 110. With the exception of the eye tracking system 112,which is addressed in more detail below, the laser surgery system 100 issubstantially similar to the laser beam modulating apparatus disclosedin U.S. Pat. No. 5,624,437, previously incorporated by reference herein.

More particularly, the computer system 110 includes a computer 114including a microprocessor, a video controller board 116, a DMDcontroller 118 which is capable of individually manipulating the mirrorsof the DMD 106 into either an ON or OFF position, and a video monitor120. The computer system 110 is capable of controlling the videocontroller board 116, monitoring and controlling external devices(safety switches, surgery footswitch, shutters, laser interface, etc.),and providing information to the user. A current preferred computer 114is a Dell Workstation Model 6550, with Dual 550 MHZ Pentium III XeonProcessors, 128 Mbytes of RAM, and 9.1 GByte SCSI hard drive, thoughother computers can likewise be used. The video controller board 116,e.g., the LCD555PCI video card available from Inside Technology (P/N710920), supplies video signals to the DMD controller 118 as well as tothe video monitor 120. The DMD controller 118 includes a video receivercard, preferably a Texas Instruments, Inc. XGA video receiver card (P/N4186152-0001), which receives video information from the videocontroller board 116 and a video driver card, preferably a TexasInstruments, Inc. XGA video driver card (P/N 4186137-0001), whichconverts the video information into signals that drive the appropriatemirrors in the DMD 106 to the ON or OFF state. The DMD controller 118may be provided external of the computer 114 or may be provided as acard or set of cards within the computer.

The optical system 104 is provided between the laser 102 and the DMD 106and is preferably comprised of common, off-the-shelf optical componentsused to shape the. laser beam (this can include beam expansion,collimation and homogenization), direct the laser beam to the DMD 106for pattern control, and direct the laser beam from the DMD to thecorneal surface of the eye. Such optical systems are well-known to thoseskilled in the art. The DMD 106 is available from Texas Instruments,Inc., and is provided with a UV-transmissive window for excimer-basedrefractive surgery systems or with an IR-transmissive window for longerIR wavelength refractive surgery systems.

In accord with the invention, software is provided to the computersystem 110 which substantially controls the operation of the lasersurgery system. The software (a) receives an input from refractioncorrection tests which identify the type (myopia, hyperopia, orastigmatism) and degree of correction required, (b) generates theappropriate refraction correction profile, (c) generates an ablationpattern for each laser pulse, (d) converts the patterns to control datafor the DMD for each layer requiring correction, (e) begins theprocedure, (f) tracks the eye position and feedbacks the eye position tothe DMD controller, and (g) checks the system parameters and fires thelaser when ready. The software is developed under LabView™; however, anysuitable language (e.g., C, C++, etc.) can be used for the softwaredevelopment.

The ablation patterns, as described. in detail below, may correspond tohigh resolution emulation of current mechanically created broadbeampatterns, scanning spot patterns, corneal topography patterns, orwavefront sensor analysis patterns. The ablation patterns are providedby the computer 114 to the DMD controller 118 such that the mirrors ofthe DMD direct the laser beam to the surface of the cornea in accordwith the patterns. In addition, as the patterns are dependent solelyupon the software and the DMD, the laser surgery system is preferablyadapted to emulate, on demand, any of the broadbeam patterns, scanningspot patterns, corneal topography patterns, or wavefront-sensor analysispatterns, subject to the required data input.

As such, a single laser surgery system can be used by severalphysicians, each of whom may desire to use a different one of thebroadbeam, basic spot scanning, corneal topography and wavefront sensoranalysis approaches. All that is required to operate under a selectedapproach is to direct the software to control the computer system, andthus operate the laser surgery system, accordingly.

Broadbeam Approach

By selecting a broadbeam approach mode of operation, the mirrors of theDMD may be configured by the computer 104 and DMD controller 118 intoany broadbeam pattern. Moreover, the DMD, with its 13 or 16 micronsquare mirrors, has substantially greater resolution and produces anearly perfect circle when the image is slightly defocused at the eye.The DMD can create a circular pattern (FIG. 10), corresponding to thepreviously used mechanical iris (FIG. 3), or a rectangular pattern (FIG.11), corresponding to the previously used slit, by turning ONappropriate mirrors to produce the correct size pattern. It should beappreciated that in FIGS. 10 and 11, only two hundred fifty-six of themillion or so mirrors of the DMD are shown.

Turning to FIG. 12, more particularly, the refraction correction for theeye is recorded in the clinic and values associated therewith are inputat 200 into the system in either spectacle or corneal plane values. Thesoftware permits value entry in either form and where entry is inspectacle values, the values are converted to corneal plane values by alookup table based on the distance between the spectacle plane and thecorneal plane (typically 12.5 mm).

Based upon the clinical refraction at 200, it is determined whetherspherical correction (for treating myopia or hyperopia), at 202, orcylindrical correction (for treating astigmatism), required, or both.For spherical corrections, a multiple zone, multiple pass (MZMP)algorithm (in which each zone is corrected separately) is preferablyimplemented at 204 with respect to a lenticule equation to more closelyapproximate the aspherical nature of the cornea. As discussed below, amultiple zone, single pass (MZSP) algorithm may alternatively beimplemented by selection at 252. One preferred lenticule equation is avariation on Munnerlyn's first order equation, described below. However,for all refraction correction profiles discussed below, higher orderprofiles can be implemented. Depending on the refraction correction, acertain number of optical zones are selected for correction. Referringto FIG. 13, these zones are sized 2.5 mm, 4.0 mm, 5.0 mm, 6.0 mm, and7.0 mm in diameter and centered about the optical axis of the laserbeam. The 2.5 mm and 7.0 mm zones are always selected and are termed thepretreatment and blend zones, respectively. The 2.5 mm pretreatment zoneis indicated at 260 and is present to reduce/eliminate central islandproblems; i.e., a central plateau portion of the cornea. The 7.0 mmblend zone is indicated at 268 and is present to provide a less abrupttissue change between the correction area and the surrounding cornealstroma. The other zones are termed power zones and are used to providethe majority of the refraction correction. Power zone 1 is 4.0 mm indiameter and indicated at 262, power zone 2 is 5.0 mm in diameter andindicated at 264, and power zone 3 is 6.0 mm in diameter and indicatedat 266. For cylindrical corrections (astigmatism), only a single powerzone (typically 5 mm in diameter) is used to apply a spherical ablationvolume to the cornea.

TABLE 1 Optical Zones 2.5 mm 4.0 mm 5.0 mm 6.0 mm 7.0 mm OZ OZ OZ OZ OZ<3.0 D (30%) (100%)  (10%) 3.0-6.0 D (30%) (60%) (40%) (10%) >6.0 D(30%) (50%) (30%) (20%) (10%) Cylinder (100%) 

Table 1 describes the optical zones (OZ) used, and the percentages ofrefraction correction implemented over each optical zone for sphericaland cylindrical corrections. With respect to the 2.5 mm zone and the 7.0mm zone the percentages listed are the percentages of refractivecorrection which is preferred for correction of the eye, based upon thevariation of Munnerlyn's equation. With respect to the power zones(i.e., the 4.0 mm, 5.0 mm and 6.0 mm zone) within each level ofcorrection, the percentages for all of the power zones together totalone hundred percent, and individually are the preferred respectiverefractive correction percentages at the cornea, as inserted into thevariation of Munnerlyn's equation, as described below. Particularly, forcorrections of less than 3.0 diopters (D), one hundred percent of thecorrection is applied to the 6.0 mm zone. For corrections from 3.0 D to6.0 D, sixty percent of the refractive correction occurs in the 5.0 mmzone and forty percent of the correction occurs in the 6.0 mm zone. Forcorrections of greater than 6.0 D, fifty percent of the correctionoccurs in the 4.0 mm zone, thirty percent in the 5.0 mm zone, and twentypercent of the correction occurs in the 6.0 mm zone.

For each optical zone requiring correction, the desired depth at aparticular radius from the optical axis out to the optical zone diametercan be determined according to the following variation of Munnerlyn'sequation,${Z_{abl}(r)} = {\sqrt{R_{pre}^{2} - \frac{D^{2}}{4}} - \sqrt{R_{pre}^{2} - r^{2}} + \sqrt{\left\lbrack \frac{\left( {n - 1} \right)R_{pre}}{{\Phi \quad R_{pre}} + n - 1} \right\rbrack^{2} - r^{2}} - \sqrt{\left\lbrack \frac{\left( {n - 1} \right)R_{pre}}{{\Phi \quad R_{pre}} + n - 1} \right\rbrack^{2} - \frac{D^{2}}{4}}}$

where Z_(abl) (r) is the ablation depth of each laser pulse for a givenradius r (a known value for a given laser system), R_(pre) is thepreoperative radius of curvature and assumed to be 7.86 mm (based onaverages), D is the optical zone in millimeters and corresponds to themultiple zones listed in Table 1, n is the index of refraction for thecornea (1.3771), and φ is a lens power defined by the surgeon and is therefraction to be implemented for a zone (i.e., the percentage value fromTable 1 for a particular optical zone is used for φ).

By knowing the ablation etch depth per laser pulse at a particularradius, Z_(abl) (r) (also known as the etch depth per pulse or EDPP),the number of pulses required to complete the procedure is determined.This is done by finding the maximum depth of the ablation which occursat the center of the optical zone (radius, r=0.0 mm) and dividing by theEDPP; that is, the number of laser pulses required for correction(NLP)=Z_(abl) (0.0)/EDPP. To implement the actual laser ablation, theradius of the “iris ” for each laser pulse must be known. From thecenter of the optical zone, e.g., r=0.0 mm and etch depth,=MAX(mm) tothe maximum optical zone, where the ablation depth=0.0 mm, values areprovided for the equation, and the equation is solved for the radius, r,for each of the laser pulse required to complete the procedure ascalculated above (NLP). However, the variation on Munnerlyn's formulacannot be solved in a closed-form solution and thus an iterativeapproach, e.g., using a zero finder algorithm such as that of Zbrent orRidder, is used. From the above (that is, once the radius r is known),the “iris” size (i.e., circular pattern size) used for correction of theassociated optical zone is determined at 206. The process is repeatedfor each zone which must be corrected, and an associated “iris” size iscalculated for each laser pulse required. An exemplar screen print for amyopic treatment is shown as FIG. 14 and shows the spherical correctionrequired at 207, correction values to implement the correction at 208,and the MZMP values at 209.

Hyperopic treatment profiles are implemented in much the same way at 204and 206. However, as the tissue must be removed at the outer edges ofthe cornea, i.e., in the shape of a ring-shaped pattern 5 mm to 10 mm indiameter centered about the optical axis of the laser beam (such thatthe cornea is steepened), Munnerlyn's equation is used to solve for thiscorrection profile. In another of Munnerlyn's equations.(See CharlesMunnerlyn, Steven Koons, and John Marshall, “PhotorefractiveKeratectomy: A Technique for Laser Refractive Surgery”, J. CataractRefract. Surg., Vol. 14, January 1988), the depth of tissue removal, forhyperopia correction, at a distance r from the optical axis is given by:${Z_{abl}^{\prime}(r)} = {R_{pre} - \frac{\left( {n - 1} \right)R_{pre}}{{\Phi \quad R_{pre}} + n - 1} - \sqrt{R_{pre}^{2} - r^{2}} + \sqrt{\left\lbrack \frac{\left( {n - 1} \right)R_{pre}}{{\Phi \quad R_{pre}} + n - 1} \right\rbrack^{2} - r^{2}}}$

where Z_(abl)′ (r) is the hyperopic ablation depth of each laser pulsefor a given radius r (a known value for a given laser system), R_(pre)is the preoperative radius of curvature and assumed to be 7.86 mm (basedon averages), n is the index of refraction for the cornea (1.3771), andφ is a positive lens power (hyperopia) defined by the surgeon and is therefraction to be implemented for the typical 5 to 10 mm zone.

By knowing the ablation EDPP and determining the center, r_(cent)′ ofthe hyperopic zone (ending radius minus beginning radius divided bytwo), the number of pulses (NLP) required to complete the procedure isdetermined. This is done by determining the maximum depth of theablation at r_(cent) and dividing by the EDPP; that is, the number oflaser pulses required for correction (NLP)=Z_(abl) (r_(cent))/EDPP. Eachradius value for the profile is then found in a similar manner as thedescribed for the myopic correction discussed above. It is noted thatthere is no removal of tissue at the optical axis, yielding thering-shaped profile similar to that shown in FIG. 15, but on a largerscale.

This type of ablation cannot be achieved using an iris/slit combinationof the prior art. Rather, the prior art requires using a mask ordirecting an image of the iris/slit opening to the outer areas of thecornea. Both of these methods are difficult to implement. Yet, referringto FIG. 15, it is clear that the DMD can implement a ring-shaped patternas easily as any other pattern. As such, where hyperopia is treated,data corresponding to sizes of ring-shaped patterns for each zonerequiring correction is calculated.

Radius values for the cylinder correction (astigmatism) are determinedat 212 and 214 in much the same way as the spherical (myopic) correctionat 204 and 206. The cylinder row of Table 1 is used, which indicatesthat one hundred percent of the refractive correction occurs at oneoptical zone (typically 5 mm). An exemplar screen print for astigmatictreatment is shown as FIG. 16 and shows the cylinder correction requiredat 215, the cylinder. correction values to implement the correction at216, and the MZMP values at 217.

A combination of spherical and cylindrical corrections may be requiredfor a particular eye. Therefore, once the sizes for “iris”, “slit”, andring-shaped patterns are calculated for the eye, the respective data forthe sizes and shapes of corrections are organized, at 218, as a sequenceof data arrays representing the order of refractive correction for thecornea for a particular optical zone. For example, it may be desirableto make the entire astigmatic correction prior to any myopic orhyperopic correction. In such case, the data for the astigmaticcorrection is positioned first, and the data for myopic or hyperopiccorrection is positioned in a trailing position. Alternatively, the dataarrays for the astigmatic and hyperopic or myopic corrections may beinterleaved. Regardless, it is preferable that the data for thecorrections be provided into data arrays which are associated with theorder in which corrective laser ablation patterns are to be provided tothe cornea.

Based upon the data arrays and the sequence of the data arrays, imagesrepresenting the desired ablation profile for the laser beam at eachlayer of the cornea are created at 220 to 224. More particularly, at220, for each ablation layer requiring spherical correction, an irissubroutine in the software is used to create a 1 bit or dichromaticmulti-pixel image (Pixmap) which emulates that of a prior art mechanicaliris or a ring-shaped pattern. Such images are similar to those shown inFIGS. 10 and 15, but will vary in size depending upon the amount ofcorrection and the zone being corrected. At 222, for each ablation layerrequiring cylinder correction, a cylinder subroutine in the software isused to create a 1 bit Pixmap which emulates that of a prior artrectangular mechanical slit pattern. Such images are similar to thatshown in FIG. 11, but will vary in size depending upon the amount ofcorrection and the zone being corrected. After the rectangular patternis created, a cylinder angle subroutine of the software is used at 224to rotate the cylinder Pixmap to the required corrective axis angle.Preferably, the results from subroutines 220, 222, 224 are merged at 226into a single Pixmap image file for each ablation layer containing datafor an image for each pulse of the laser during each pass.

Once the Pixmap images are created, the actual laser surgery procedurecan begin. Generally, the patient is placed under a microscope andpositioned correctly for the procedure and the physician preps thepatient at 228. Prepping includes using a photorefractive keratectomy(PRK) or laser keratomileusis in situ (LASIK) technique. That is, ineither technique the corneal stroma must be exposed prior to providing alaser beam to the cornea for corneal reshaping. In PRK, the epitheliumof the cornea (approximately 40 to 55 microns) is removed by anyeffective means, e.g., with a laser, by scraping, or by chemical means,to expose the endothelium. In LASIK, a flap is cut approximately 120 to160 microns deep into the corneal stroma, and the flap is flipped backto expose, the corneal stroma. The physician then reviews the treatmentprofile and begins the procedure.

The software then translates the Pixmap images into DMD mirror positiondata. At 230, the DMD receives the data and individual mirrors of theDMD are identified to be in respective ON or OFF positions such thattogether the mirror array forms a pattern which simulates the Pixmapimage. As stated above, when the patterns produced by the mirrors areslightly defocused on the cornea, the patterns are of very highresolution and substantially greater resolution than the patternsdefined by the prior art mechanical devices.

At the same time, the software causes the Pixmap image to be displayedat 232 on a video monitor as a dichromatic image, e.g., black and white,so that the physician may review and monitor the ablation patterns.

The eye tracking system 112 provides at 234 input to the computer 110which then directs the DMD controller 118 to compensate for thedeviation of the eye from center (or from a prior registered off-centerlocation). The feedback from the eye tracking system causes the Pixmapimage to be shifted at 236 on the video monitor, and the ON/OFF patternof mirrors is also shifted at 238 to compensate for eye movement suchthat the DMD mirror ablation pattern is always correctly directed towardthe cornea. Various systems may be used to track the movement of the eyeand provide feedback to the computer 110 and the DMD controller 118. Inone approach, disclosed in U.S. Ser. No. 09/371,195, filed Aug. 10,1999, and hereby incorporated by reference herein in its entirety, theeye tracking system 112 uses a CCD camera connected to the surgicalmicroscope, an illuminator to illuminate the eye, and an algorithm tofind the center of the pupil and compare it against the starting pointof the procedure. The eye tracking system 112 is able to continuallyfeed the eye movement information to the computer 110 in order to offsetthe refraction correction pattern created by the mirrors of the DMD 106such that the pattern is directed to the correct position based on theeye's last position. Other approaches to tracking the eye may also beused. For example, and not by way of limitation, target markers placedon the cornea (reflective or absorptive to certain wavelengths) may bemonitored, laser spots aimed at the cornea (typically infrared energy)and monitored by a camera or other electronic means (such as Quaddetectors) may be tracked, anterior physiological structures, such asthe limbus, may be tracked, or the retina may be tracked.

In parallel with the operation of the eye tracker 112, the computersystem checks all of the system parameters (including, but not limitedto, laser status, safety switch status, gas cabinet sensor status (forgas-based lasers), safety shutter subsystem status, laser energy sensorstatus, nitrogen flow status, surgeon footswitch status, emergency stopswitch status, surgeon joystick control status, exhaust plume tubeposition, and status indicator lights). Once the system checks have allbeen confirmed, the surgeon is able to fire a laser pulse (typically viaoperation of a footswitch).

When the laser 102 is fired at 240, it is shaped and conditioned by theoptical'system 104, and directed onto the mirror array of the DMD. Thelaser beam is then reflected at 242 by the mirror array. Each mirroreither reflects its associated portion of the laser beam pulse eitheraway from or towards the cornea according to the respective ON or OFFposition of that mirror. As such, the desired ablation pattern isreflected toward the eye. Additional optics then image at 244 thepatterned laser beam onto the eye, preferably in a demagnified ratio.

This procedure continues at 230 and 232 for subsequent layers ofablation until all layers (pulses) have been delivered for a givenoptical zone being corrected. Then, in an MZMP procedure, the requiredcorrection to the other zones are implemented on the patient cornea insubsequent respective “passes” (i.e., pulses of the laser on anassociated DMD mirror pattern), preferably with a slight pause betweeneach pass for inspection of the eye.

At the conclusion 250, the resultant etch is aspheric in shape, andrepresented by the chart of FIG. 17, in which the ablation for theindividual zones is illustrated in light lines (2.5 mm pretreatment zoneat 260, 4 mm power zone at 262, 5 mm power zone at 264, 6 mm power zoneat 266 and 7 mm blend zone at 268), while the total ablation resultingfrom the combination of individual zones is illustrated in a bold lineat 270.

While a MZMP approach has been described above for the broadbeamemulation, alternatively, the Pixmaps for the DMD pattern generation canbe defined to ablate across multiple zones in each pass. To that end, at252 in FIG. 12, the multiple zone, single pass (MZSP) approach may beselected. Upon selection of the MZSP approach, the spherical andcylinder position data arrays for each zone are merged into a singlearray representing a combination of all of the treatment zone profiles.In accord with one manner of implementing the MZSP approach, all zonesand their profiles are merged, by summing, into the graph curve 270 ofFIG. 17. However, the graph curve 270 has a plurality of transitionpoints 272 a, 272 b, 272 c which it is desirable to eliminate (i.e.,smooth over). These transition points are not as severe as those createdwith prior art irises and slits in a broadbeam approach. Nevertheless,any transition point may subject the corrected eye to glare or haloeffects.

Therefore, for a MZSP approach, it is more preferable that a curveassociated with the resulting graph curve 270 be generated in which avery smooth ablation profile without transition points is provided, suchas shown in FIGS. 26a and 26 b. In accord therewith, a second manner ofimplementing the MZSP approach is provided in which a dynamic polynomialequation mimics the multizone profile, but is based solely on therefractive correction (diopter). The dynamic polynomial equation isdetermined by first classifying required corrections according to theirseverity. For corrections more severe than −6 diopters, the multizonemethod uses five zones (including the pretreatment and blend zones), forcorrections between −3 diopters and −6 diopters four zones are used, andfor corrections less than −3 diopters three zones are used. Referring toFIG. 27, for each of the three classifications of correction severity,several profiles are generated that cover the full range of thatclassification. Second, a graph compiling the data into a format thatcan be translated for establishment of a trendline is created. This canbe done with any of several software packages, such as Microsoft Excel®or National Instruments Hi-Q™. Third, as shown in FIG. 28, a trendlineis established for each of the profiles. The equations for thetrendlines (shown in FIG. 28) must closely follow the contours seen inFIG. 28. Polynomial curve fit equations are preferably used for thetrendlines, although other curve fits, e.g., the error function erf (r),may be used as well. It has been found that sixth order polynomialequations accurately generate the required profiles. Each equationrepresents the profile of a specific correction (diopter), and theequations are dissected and the magnitude of each equation ordercomponent is graphed based on the correction, with the magnitude of eachequation order component found to be nearly linear (R²=0.9993), as shownin FIG. 29. Then, as also shown in FIG. 29, a second polynomial equationis created based on the trendline. One such polynomial, the second orderequation y=0.0015×²+0.0505×+0.0561, is shown in FIG. 29, provides adesirable fit. From this second polynomial equation, software is writtento generate a dynamic equation that generates a smooth profile based onthe desired diopter correction, and the ablation layers are slicesthrough the generated smooth profile. The software may be applied to aDMD in which a central mirror element of the DMD is selected and theradial distance values for each of the other mirrors elements isdetermined relative thereto. All of the values are then represented in amathematical array as a data file, and the procedure is then implementedin a similar manner to the previously described MZSP approach to producea 3-D ablation image (FIG. 26a) and a 2-D ablation profile (FIG. 26b)which is smooth along its length; i.e., without transition points.

In addition, while the spherical and cylinder data arrays are used tocreate the Pixmap images, the signals used to otherwise control iris andslit motors may be directly utilized and translated into the Pixmapimage data. As such, a broadbeam approach with a DMD is highlyadaptable, with configurations based upon physician requirements withoutthe mechanical limitations of the prior art.

Scanning Spot Approach

By selecting the scanning spot mode of operation, more complex,customized ablation patterns may be applied to the cornea. If theMunnerlyn approach is coupled to the previously described “iris” and“slit” patterns, in either a MZMP or MZSP format, a circular (sphericalmyopia or hyperopia) or rectangular (astigmatism) ablation pattern willbe applied to the eye. Referring back to FIG. 7, the most widely usedscan technique for directing a spot scan in accord with an ablationpattern is a raster scan, much like a television monitor scan (left toright, top to bottom). FIG. 18 illustrates another currently usedscanning method called a random scan in which the laser spot is moved ina random sequence about the cornea. This scanning method reduces anypotential adverse heating effects due to the spots being applied toonear to each other. FIG. 9 illustrates a new technique according to theinvention, termed a polar scan. In a polar scan, the spot is scanned ina circular fashion for each pulse layer. Preferably, the spots are movedin a 50/50 overlap, though other percentage overlaps may be used. Thisapproach matches the edges of the circle better than the rasterapproach. FIG. 20, also a new technique, illustrates a polar method withthe addition of a rotation (here shown at 20°, though other rotationalangles may be used). As such a plurality of sectors are scanned insuccession. FIG. 21, yet another new technique, illustrates aclosed-pack method in which a hexagonal approach is used to cover anarea more efficiently. Preferably, in a closed pack, there is no overlapof the laser spots. In any of these methods, the overlap of the spotsmay be adjusted to optimize the resulting etch profile and scanning mayoccur from the center outward or from the periphery inward.

The software enables the DMD to emulate any of the corrective eyepatterns and scanning spot methods (raster, random, polar, closed-pack,and others not described) used in a conventional scanning spot approach,in either of two modes.

In a first mode (spot mode), the scanning spot approach can be emulatedby turning ON enough mirrors (e.g., a 30 by 30 to 60 by 60 array ofmirrors) to create a typical scanning spot laser diameter (e.g., 0.5 mmto 1.0 mm). Alternatively, fewer mirrors can be turned on such that the“spot” is much smaller than typical scanning spots and substantiallybetter resolution can be achieved. This “spot” is then moved across thecornea in any scanning method (e.g., raster, random, polar, polar withrotation and closed-packed) by turning ON and OFF the appropriatemirrors to simulate offset or scanning of the spot across the DMDdevice.

In a second and more preferred mode (layer mode), the software directsthe DMD to implement an entire ablation layer in a single laser pulse,by turning ON the appropriate mirrors to simulate the resulting etchpattern which would otherwise be created after all scanned spots havebeen delivered for a particular ablation layer in the spot mode. In thismanner, any concern present regarding the effects of interruption ofconventional scanning spot system are eliminated, as an entire layer isablated at once.

More particularly, referring to FIG. 22, the scanning spot emulationmethod is initially similar to the broadbeam approach. That is, clinicalrefraction tests are carried out at 300 to determine the degree ofcorrection needed. Next, the spherical correction is determined at 302and a lenticular equation (first or higher order) is used to generate at304 a spherical correction profile. Likewise, a cylinder correction isdetermined at 310 and a lenticular equation is used to generate at 312 acylinder correction profile.

The spherical and cylinder correction profiles are combined to result inan initial correction at 314. Preferably, though not required, thescanning spot emulation additionally accounts for corneal topographydata. As such, a topographer 130 (FIG. 9), e.g., a Keratron CornealAnalyzer manufactured by Optikon 2000 of Rome, Italy, is used at 316 todetermine the actual topography of the cornea. The topographer generatesa Pixmap image of corneal height data at each pixel of the image. ThePixmap image is preferably 8 bit, through other resolutions may be used.Based upon the actual topography of the cornea, an “ideal” topographicalprofile is generated at 318. The ideal profile corresponds to an idealspherical or aspherical fit provided by the topographer throughmathematical modeling. The difference between the actual profile and theideal profile is then calculated at 320 to produce a difference profile.The difference profile is a Pixmap image indicating the difference inheight between the ideal and actual profiles at each pixel. Next, thedifference profile is combined with the initial correction profile toresult in a final correction profile.

Based upon the etch depth per pulse (EDPP), Pixmap images are thengenerated at 324 for each etch slice or layer from the final correctionprofile. The Pixmap images for each layer are 1 bit images, and dataassociated with a sequence of the Pixmap images corresponding to theentire laser ablation procedure is stored in memory in the computersystem.

Where the system seeks to directly emulate a spot scanning system (i.e.,such that each laser pulse ablates a single pixel-sized spot of alayer), each Pixmap image is divided at 326 into a number of spots witha particular percentage overlap and spot layout (raster, random, polar,closed-pack, etc.), which is also stored as data. Where moving spotemulation is not desired (i.e., such that an entire layer will beablated for each laser pulse), no such division is required and step 327is implemented.

At this point, the actual laser surgery procedure can begin and thepatient is prepped at 328, as discussed above. The Pixmap spot (whenstep 326 is implemented) or entire Pixmap image (when step 327 isimplemented) representing the initial location for ablation is thenloaded at 330 into a buffer of the computer system 110. The eye trackingsystem 112 then calculates the. movement of the eye and manipulates thebuffered data such that the spot or image is translated accordingly. ThePixmap image is displayed at .334 on a video monitor 120 and the mirrorsof the DMD are also arranged at 336 in an ON/OFF pattern to simulate thePixmap image. The laser is then fired at 338 at the DMD mirror array.

When the laser 102 is fired at 338, it is shaped and conditioned by theoptical system 104, and directed onto the mirror array of the DMD. Thelaser beam is then reflected at 340 by the mirror array. Each mirrorreflects its associated portion of the laser pulse either away from ortowards the cornea according to the respective ON/OFF positions of themirrors. Additional optics then image at 342 the patterned laser beamonto the eye, preferably in demagnified ratio.

The procedure then continues at 330 for subsequent spot locations (wherethe system performs individual spot scanning emulation at 344) and/orfor other layers of ablation (in both spot scanning mode and layer mode)until all layers have been treated in each optical zone requiringcorrection at 346. The resulting etch at 348 has per pixel resolution ofthe Pixmap image and is adapted to correct corneal topography defects.Depending upon the spot size, the procedure provides correction with aresolution at least as sharp as that of prior art systems. See, forexample, scanning spot ablation patterns shown in FIGS. 8(c) and 8(d).With relatively smaller spots, greater resolution is achievable.

Corneal Topography Layer Approach

While a scanning spot system utilizing corneal topography providessuperior results to broadbeam and traditional scanning spot approaches,any scanning spot approach is hindered in that its resolution is limitedby the size of the scanned spot and the overlap of spots in a scanningspot approach. In response to this limitation, a corneal topographylayer approach optimized for use with a DMD is now described.

Referring to FIG. 23, the procedure is substantially similar to theabove described spot scanning approach utilizing corneal topographydata. As such, steps 400 to 422 correspond exactly to steps 300 to 322in FIG. 22, which ate described above. In accord with the presentapproach, after the final correction profile is obtained at 422, basedon the etch depth per pulse (EDPP), the computer 110 divides the finalcorrection profile into layers at 424. Each layer is converted at 426into a 1 bit Pixmap image which is stored as data in a memory of thecomputer 110. At this point, the procedure continues and steps 428 to442 correspond exactly to steps 328 to 342 in FIG. 22. After the laserbeam is imaged at 442 onto the eye in the pattern of the Pixmap imagefor treatment of a particular correction layer, if at 444 there areadditional layers requiring treatment, the procedure continues at 430.If at 444, no other layers require treatment, the procedure is completedat 446. As shown in FIG. 24, this approach (using 13 or 16 micronmirrors) can better match the corneal topography and other correctionrequirements than'scanning spot systems (using a 0.5 mm or 1 mm spot).It is noted that this approach provides a resolution approximately 60times the resolution of prior art scanning spot systems.

Wavefront Sensing Approach

By selecting the wavefront sensor mode of operation, the most advancedsystem for laser refraction is enabled. In order to select this mode,the laser surgery system 100 must be coupled to or adapted to receivedata from a wavefront sensor system 140 (FIG. 9). The wavefront sensorsystem 140 analyzes the optical system of the eye 108 and provides datacorresponding to a three dimensional representation of the opticalsystem of the eye. The three dimensional results are translated into anarray of optical wavefront data that characterizes the entire opticalsystem of the eye. This information is preferably either in the form oftopographical data (i.e., the height values that need to be corrected toarrive at an optimized corneal shape) or in optical power data (oftenreferred to as K-readings). One such wavefront sensor system isdisclosed in U.S. Pat. No. 5,777,719 to Williams, which utilizes aHartmann-Shack sensor and which is hereby incorporated by referenceherein in its entirety, and others are available or forthcoming from20/10 Perfect Vision of Heidelberg, Germany; Technomed GmbH ofBaesweiler, Germany; Bausch & Lomb Surgical of Claremont, Calif.; andTracey. Technologies of Bellaire, Tex.

Here, a visible laser beam, or a number of visible laser beams, aredirected through the entire eye optical system: cornea, lens, vitreousand retina. The return reflection from the retina is recorded by a CCDcamera and analyzed against an ideal wavefront. Thus, the entire opticalsystem is analyzed. According to the invention, the result of thisanalysis, rather than providing data for creating an ideal topographicalprofile or initial correction profile (as is done in corneal topographydriven systems), provides data which is directly used to control etchingof the cornea.

Therefore, the laser refractive correction procedure will proceed muchlike that described above with respect to the corneal topography layerapproach described above. The main difference is in the configuration ofthe wavefront analysis system: offline or real-time. In the offlineapproach a series of layers are generated before the surgery, stored andthen used to guide the laser ablation to the cornea, as is done in thecorneal topography layer approach. In the real-time approach thewavefront sensor is built into the refractive laser system and evaluatesthe cornea after every layer (or a sequence of layers) is ablated. Thiscontinues until feedback from the wavefront sensor indicates that thecornea has been modified to properly correct for aberration in theoptical system of the eye.

Referring to FIGS. 9 and 25, according to the wavefront sensor approach,in either the off-line or real-time approaches, the wavefront sensorsystem 140 measures the eye system aberrations and creates a 3-D contourprofile (substantially similar to FIG. 8(a)) and data correspondingthereto is input at 502 into the computer system 110. The computersystem then divides or slices at 504 the contour profile (3-D data) intolayers (a series of 2-D data points) based on the EDPP. Each layer isconverted at 506 into a 1-bit Pixmap image and stored as layer data in amemory of the computer system 110. The surgeon then preps at 508 thepatient for laser refractive surgery (PRK or LASIK). The appropriatelayer data is then loaded at 510 into a buffer. The eye trackercalculates movement of the eye and adjusts or translates at 512 thePixmap image accordingly. The translated Pixmap image is displayed at514 on the video monitor 120, and also provided at 516 to the DMD 106through the DMD controller 118 such that the DMD simulates the Pixmapimage. The laser beam is directed at 518 to the DMD mirror array surfaceand then reflected at 520 by the DMD surface toward the cornea in accordwith the Pixmap image. Optics image at 522 the reflection onto the eye,preferably at a demagnified ratio. In real-time mode, the procedurerepeats at 500, with a subsequent wavefront sensor analysis of the eyesystem. The process is repeated until the wavefront sensor analysisconfirms that the eye system has been corrected within a preferredmargin of error. In off-line mode, the procedure continues at 510 withthe loading of the next. layer for correction. In either mode, at 526,once all layers have been etched the entire optical system of the eye iscorrected with per pixel resolution.

Each of the offline and real-time approaches are disclosed in moredetail in previously incorporated parent application U.S. Ser. No.09/524,312.

In view of the above, a laser surgery system is provided which isadaptable to emulate and/or perform every currently used approach tolaser surgery. That is, as the techniques are controlled by softwarecoupled to a DMD and not limited by hardware requirements, a singlelaser surgery system may be used to operate according to any of theabove described approaches. Moreover, unlike any prior art system, thelaser surgery system can directly match corneal topography or wavefrontsensor data “point-to-point” from data points to individual DMD mirrors.That is, since corneal topography and wavefront sensor systems are bothdigital in nature and offer 2-D digital information, the digitalinformation may be directly mapped to the 2-D array of mirrors of theDMD. Furthermore, the laser surgery system is capable of providingsignificantly greater resolution than prior art systems as theindividual mirrors of the DMD are 13 or 16 microns in size. As DMDsbecome available with greater numbers of mirrors of smaller size, theresolution of the techniques described herein will likewise beincreased.

There have been described and illustrated an embodiment of a lasersurgery system and methods of using the same. While particularembodiments of the invention have been described, it is not intendedthat the invention be limited thereto, as it is intended that theinvention be as broad in scope as the art will allow and that thespecification be read likewise. Thus, while particular prior art systemshave been described for emulation, it will be appreciated that othersystems may be emulated as well. In addition, while particular types ofscanning methods have been disclosed, it will be appreciated that otherscanning methods can be used as well. Also, while a laser surgery systemwhich can emulate all of the broadbeam, corneal topography scanningspot, and wavefront sensor scanning spot techniques has been described,it will be appreciated that a laser surgery system which emulates onlyat least one of the techniques can be provided, as such will include theadvantage of the superior resolution provided by the DMD. As such, whileit is preferable that a corneal topographer or a wavefront sensor systembe included in the laser surgery system, neither is required. Inaddition, while the invention is described with respect to a variationof Munnerlyn's equation, the unvaried Munnerlyn's equation (bothcollectively referred to as Munnerlyn's equation in the claims) or anyother lenticule equation, e.g., Schwiegerling's higher order equation,may be used. Moreover, while a number of scanning methods with differingoverlaps have been disclosed, it will be appreciated that no overlap isrequired in any scanning spot emulation, due to the relatively highresolution of the DMD and the ability to slightly defocus at the cornea.Furthermore, while particular orders of steps for the methods (as shownin the flowcharts) are preferred, it will be appreciated that the stepscan be performed in another order. It will therefore be appreciated bythose skilled in the art that yet other modifications could be made tothe provided invention without deviating from its spirit and scope asclaimed.

What is claimed is:
 1. A laser surgery system for reshaping the corneaof the eye, said system comprising: a) means for generating smoothablation curve profile data which does not include transition points andwhich corresponds to a desired correction for the eye, said smoothablation curve profile data being based on a single at least sixth orderpolynomial equation; and b) a laser adapted to reshape a portion of acornea of the eye according to said profile data.
 2. A laser surgerysystem according to claim 1, further comprising: c) a digitalmicromirror device (DMD) having a plurality of mirrors adapted tomodulate a laser beam produced by said laser such that the cornea of theeye is reshaped without transition points.
 3. A laser surgery systemaccording to claim 1, wherein: said laser is a broadbeam laser.
 4. Amethod of directing mirror of a digital micromirror device (DMD) used ina laser eye surgery system having a computer, comprising: a) inputtingeye refraction data into the computer; b) generating with the computer arefraction correction profile polynomial equation; c) generating asequence of ablation pattern images to implement the refractioncorrection profile; and d) converting the sequence of ablation patternimages into control data which configures the mirrors of the DMD intothe ablation patterns.
 5. A method according to claim 4, wherein: adiopter correction is used to generate coefficients for said refractioncorrection profile polynomial equation.
 6. A method according to claim4, wherein: said at least one polynomial equation is based upontrendlines established for each of a plurality of ranges of requiredcorrection.
 7. A method according to claim 4, wherein: said refractioncorrection profile polynomial equation is a sixth order equation.
 8. Amethod according to claim 4, wherein: said ablation patterns are createdin a manner which emulates a scanning spot laser surgery system.
 9. Alaser surgery system according to claim 1, wherein: said single sixthorder polynomial equation includes coefficients defined by second orderpolynomial equations.
 10. A laser surgery system according to claim 9,wherein: each of said coefficients is related to a respective dioptercorrection.
 11. A method of generating an equation for a refractioncorrection profile of an eye having an optical aberration, comprising:a) determining zones of optical correction for the eye; b) for eachzone, determining a set of data points; c) summing the set of datapoints to define a curve with a plurality of a transition points; d)determining a sixth order polynomial equation that approximates thecurve with the plurality of transition points, the sixth orderpolynomial equation having a plurality of coefficients; and e) using atleast one at least second order equation to establish values for theplurality of coefficients for the sixth order polynomial equation, saidsixth order polynomial equation and said plurality of coefficientstogether defining the refraction correction profile.
 12. A methodaccording to claim 11, wherein: said data points for each zone arecreated with Munnerlyn's formula.
 13. A method according to claim 11,wherein: said at least one at least second order equation is at leastone second order equation.
 14. A method according to claim 11, wherein:said sixth order polynomial equation is determined through a curvefitting technique.